Targa versus PNG for Image Texture
PNG takes longer to read or write, because the computer needs to compress it. Therefore it takes up less space. TGA is largely uncompressed, so it's being written and read faster, but takes up more space. Both formats are loss-less, but I think the color range of TGA is larger.
Targa is popular in Game Enginges because the Alpha channel is independent from the color channels and it reads very fast. EXR is usually the largest, but it supports HDR. I haven't tested it, but it should be read faster than PNG.